1. Field of the Invention
The present invention relates to an optical disc and a recording and reproducing apparatus, particularly, relates to an optical disc and a recording and/or reproducing apparatus for the optical disc having a copy-protection function.
2. Description of the Related Art
A description is given of the prior arts referring to the accompanying drawings.
FIG. 1 is a fragmental plan view showing a plurality of information pit rows formed on an optical disc in the prior art;
FIG. 2 represents a relation between an information pit width and a light intensity distribution of a laser beam in the prior art;
FIG. 3 is a block diagram showing a flow of recording signal in the recording device in the prior art; and
FIG. 4 is a block diagram showing a flow of reproduction signal in the reproducing device in the prior art.
In FIG. 1, a reference character 11 designates a first information pit row, 12 a second information pit row, 13 a third information pit row, 11A a first information pit, 11B a second information pit, 11C a third information pit, L.sub.11A a first information pit length, L.sub.11B a second information pit length, L.sub.11C a third information pit length, P.sub.11AB an interval between the first information pit 11A and the second information bit 11B, P.sub.11BC an interval between the second information pit 11B and the third information pit 11C, "W.sub.K " a width of each of the information pits 11A, 11B, 11C, "q" a pitch between neighboring information pit rows.
In FIG. 2, a reference character 14 designates a recording master disc, 15 a photo-resist, 16.sub.K the information pit, and 17.sub.K a light intensity distribution curve of a laser beam.
In FIG. 3, a reference character 50 designates a recording device, 51 an encoder, 52 a photomodulator, and 52a a laser beam carrying a series of recording codes.
In FIG. 4, a reference character 55 designates a reproducing device, 56 a CD (Compact Disc), 57 an optical pickup, 58 a RF amplifier, and 59 a decoder.
Next, a description is given of an outline of an optical disc apparatus for the CD recorded with music as an example.
First of all, an outline of a recording by using the recording device 50 for the CD, i.e., an outline of a master disc cutting, is described as follows:
As shown in FIG. 3, sound signals are converted into a predetermined digital data by an A/D converter (not shown) and the digital data are inputted to the encoder 51. These digital data are converted into a waveform string on the basis of predetermined conversion rules by the encoder 51. This waveform string is inputted to the photomodulator 52. This waveform string is amplified by the photomodulator 52, and is converted into a series of recording codes for driving a laser generator (not shown). The laser generator generates a laser beam 52a carrying a series of recording codes as an intensity modulated light beam in response to the series of recording codes. The photo-resist 15 coated on the recording master disc 14 is exposed to the laser beam 52a carrying the series of recording codes, so that exposed portions to become information pits are formed in accordance with the series of recording codes. Thus, an information pit pattern is formed on the photo-resist 15 by causing the photo-resist 15 to be developed. From the recording master disc 14 provided with the photo-resist 15 having the information pit pattern, a stamper (not shown) is formed through predetermined processes. A replica of the information pit pattern formed on the photo-resist 15 is transferred to a polycarbonate substrate by injection-molding of polycarbonate resin, using the stamper as a metal mold. Thus, the CD 56 is obtained by performing a predetermined process on the polycarbonate substrate.
Next, a description is given of a shape of the information pit.
In FIG. 1, there are shown the first, second and third information pit rows 11, 12, 13 on the CD 56 as examples of the information pit rows. The information pit rows 11, 12, 13 are disposed along a single spiral track having a pitch between the information pit rows being is made a fixed value of "q".
A width of each of the information pits 11A, 11B, 11C . . . of which the information pit rows 11, 12 and 13 are composed, has a fixed value "W.sub.k ", but lengths L.sub.11A, L.sub.B L.sub.11C . . . thereof and intervals P.sub.11AB, P.sub.11BC, thereof are subject to change corresponding to the series of the recording codes.
The width "W.sub.k " of each of the information pits 11.sub.A, 11.sub.B and 11.sub.C . . . is determined by a light intensity distribution 17.sub.k of a laser beam used to irradiate the photo-resist 15 on the recording master 14. Specifically, in FIG. 2, the laser beam 52a has the light intensity distribution 17.sub.k, wherein the ordinate represents an intensity of the laser beam (spot) and the abscissa represents a radial position of the recording master disc 14 or the CD 56. When a width of the laser beam having a light intensity more than a threshold value for exposing the photo-resist 15 is "W.sub.k ", a domain of the photo-resist irradiated with the laser beam having the light intensity more than the threshold value is turned into an exposed portion having a width of "W.sub.K ". The exposed portion is soluble in a development solution due to a photo-chemical reaction, so that it becomes a pit 16.sub.k caused by a predetermined development process. Thus, the information pit rows are formed corresponding to the series of recording codes.
On the other hand, the lengths L.sub.11A, L.sub.11B, L.sub.11C . . . of the information pits and the intervals P.sub.11AB, P.sub.11BC, . . . therebetween are determined by a high intensity duration and a low intensity duration (OFF when a threshold control is provided) of the laser beam, respectively.
Next, a description is given of an outline of the reproducing apparatus 55.
As shown in FIG. 4, the information pit rows on the CD 56 are constantly irradiated with the laser beam by a laser element which is one of components of the optical pickup 57. As a result, the irradiated laser beam is reflected from a surface of the CD 56 as an intensity modulated beam of light responsive to positions and shapes of the information pits. Reproduction signals are obtained by the optical pickup 57 which detects thus modulated reflected beam of light.
The reproduction signals are inputted to the RF amplifier 58. After amplified thereby, the reproduction signals are outputted as a waveform string and are inputted to the decoder 59 after having subjected to a wave equalization and to a discriminating process (not shown).
From the decoder 59, a series of data are obtained by an inverse conversion of the series of codes recorded on the CD 56, and the series of data are converted into sound signals by a D/A converter (not shown).
When music information such as above and picture or character information is in a form of digital information, quality of the information is not degraded upon copying or transferring the information because of an inherent characteristic of the digital information transmission, compared with analogue form thereof, this causes a problem of infringement of copyright. Thus, it is required to inhibit or to limit a perfect copy of the digital information as it is (referred to as a digital copy hereafter). For example, there is proposed a countermeasure referred to as the Serial Copy Management System (SCMS) adopted to the Mini Disc (MD) against the digital copy.
In the SCMS, a protect code (or a key code) for copy permission or copy inhibition is included in a part of digital information recorded on the MD, and when the digital copy is performed of the MD, the copying the MD beyond one generation is intended to be inhibited by causing an MD apparatus to refer the protect cord.
Specifically, the protect code is written within an area of a table of contents (referred to as TOC). If a code of "non-protect" is written in the TOC of the MD, the MD is able to be copied. When the MD has been copied onto a first generation copy, a code of "protect" is written in its area of TOG. If the code of "protect" is written therein, the MD is unable to be copied to produce a second generation copy. Thus, the MD is prevented from being copied in two or more generations.
In the above SCMS, the protect code is written in the part of the information recorded in the MD, and the copy permission or the copy inhibition of the MD is determined by the MD apparatus referring to the protect code written in the TOC. Thus, in a case where the information recorded on the MD is directly read out as it is without decoding and the information read out is written in another disc as it is, the information including the protect code can be copied as it is regardless of the contents of the protect code. This enables the MD to be copied through many generations, thus, the illegal copying can not be prevented by the SCMS.